How do you make your model skeleton to look like this?
In this case it looks the importer has created tiny bones at each of the pivot points, and the lines you are seeing correspond to parent-child relationships between them.

Tiny bones, empties instead of bones or disconnected/misaligned bones are a common quirk of many file importers/versions of file types. Unfortunately for file types like fbx and collada, there are many small variants of them that make writing importers very tedious.

This is most likely to happen because some data is missing or slightly different than expected in the file format, and should really be considered a bug in the importer. Either way, bone length is a visual convenience and has no effect on the calculations used to deform the model. Small bones do make it harder to select and manipulate though. If the bones have a different orientation, then this can be a problem for some constraints like IK.

To solve this you can try using different importer settings or file formats if they are available, possibly importing and re-exporting through other software.